Hard disc drives enable users of computer systems to store and retrieve vast amounts of data in a fast and efficient manner. In a typical disc drive, the data are magnetically stored on one or more discs which are rotated at a constant high speed and accessed by a rotary actuator assembly having a plurality of read/write heads that fly adjacent the surfaces of the discs.
The position of the heads is controlled by a closed loop, digital servo circuit. A preamp and driver circuit generates write currents that are used by the head to magnetize the disc during a write operation and amplifies read signals detected by the head during a read operation. A read/write channel and interface circuit are operably connected to the preamp and driver circuit to transfer the data between the discs and a host computer in which the disc drive is mounted.
Disc drive manufacturers typically produce a large number of nominally identical drives which are individually optimized during the manufacturing process through the setting of parameters that affect the operation of various disc drive circuits, such as the preamp and driver circuit, the servo circuit and the read/write channel. Such parameters are well known and typically include write current, write precompensation, servo gain, data and servo level detection thresholds, transversal equalizer tap weights, adaptive filtering parameters and, in disc drives employing magneto-resistive (MR) heads, read bias current. Such parameters are used to enable the disc drive to accommodate changes in data transfer rates that occur with respect to the radii on the discs at which the data are stored, noise levels, electrical and mechanical offsets and the like, all of which generally affect the operation of the drive.
Accordingly, the parameters are often set to an initial value during disc drive operation and then optimized against predefined acceptance criteria (for example, measured read error rate). Disc drives are often further provided with the capability of continually monitoring drive performance and adjusting certain parameters adaptively during operation to maintain optimum levels of performance.
One of the most significant variables affecting disc drive performance is temperature. Disc drives are complex electromechanical devices which include motors to rotate the discs and the actuator assembly. Although such motors are designed to operate efficiently, heat will nevertheless be generated as the disc drive operates over an extended period of time, which can substantially increase the operating temperature of the drive. Disc drives further include one or more processors and associated integrated circuitry having performance characteristics which are also affected by changes in temperature.
Attempts have been made in the prior art to compensate for variations in temperature in magnetic recording devices such as disc drives. For example, U.S. Pat. No. 3,723,980 entitled TEMPERATURE COMPENSATION SYSTEM FOR A MAGNETIC DISK MEMORY UNIT issued Mar. 27, 1973 to Gabor compensates for variations in temperature through efforts to maintain a substantially uniform temperature and by using similar materials in similar locations within a drive. U.S. Pat. No. 5,408,365 entitled RECORDING DEVICE WITH TEMPERATURE-DEPENDENT WRITE CURRENT CONTROL issued Apr. 18, 1995 to Van Doom et al. discloses a magnetic tape device wherein a magneto-resistive head element in contact with a recording tape media is used to monitor the temperature of the media, enabling adjustments in write current magnitude accordingly. U.S. Pat. No. 5,550,502 entitled CONTROL CIRCUIT AND METHOD FOR THIN FILM HEAD WRITE DRIVER issued Aug. 27, 1996 to Aranovsky discloses a write driver control circuit in a magnetic storage device that provides sufficient range in the input voltage level to accommodate temperature and process variations during the operation of the device. U.S. Pat. No. 5,455,717 entitled RECORDING DEVICE WITH TEMPERATURE-DEPENDENT WRITE-CURRENT CONTROL issued Oct. 3, 1995 to Van Doom et al. discloses a compensation circuit for controlling the amplitude of the write current in relation to temperature variations within a drive.
These and other references generally teach either the use of various disc drive materials that are not significantly affected by temperature variations during operation, or such references generally teach to periodically measure the temperature of the disc drive and adjust various parameters accordingly. Such temperature measurements are performed using existing components of the recording devices (such as read heads in contact with magnetic tape media) or discrete temperature sensors which are mounted either inside the environmentally controlled housing of the disc drive, or on an externally mounted printed wiring assembly (PWA) of the drive.
Although such prior art approaches have been operable, there remains a continual need for improvements in the art whereby disc drive performance can be efficiently and readily optimized in response to variations in the temperature of a disc drive for a wide range of temperature-dependent disc drive parameters.